1. The Prior Art
Although plastics are produced in large quantities only since about 1930, they have become indispensable now for modern life. However, the rapidly expanding production and increasing consumption of plastic materials are increasingly posing problems. In the foreground is in particular the pollution of the environment with plastic refuse. Known statistical data show that the component of plastic refuse is alarmingly high: about 18% of the volume of municipal refuse is caused by plastic materials, with about half of that volume being attributed to packaging refuse. The disposal of plastic materials continues to be extremely problematic in this connection, for example because highly toxic dioxins may be formed in the incineration of such materials. In the USA, approximately 96% of the total amount of plastic refuse ends up in garbage dumps, 3% is incinerated, and only about 1% is recycled.
The search for an equivalent substitute material becomes more and more urgent because the demand for plastic materials is constantly growing. There is consequently an extraordinarily high demand for biodegradable materials that offer the advantages of plastics, but are nonetheless biodegradable at the same time.
Attempts have been increasingly made in the last few years to meet these requirements. However, it has been found that the realization is connected with huge problems due to the fact that the required properties are mutually exclusive in most cases.
A possible solution is described in EP 0 696 605 A1, which relates to a biodegradable multi-block polymer, which is prepared by linear polycondensation of two .alpha., .omega.-dihydroxy polyesters/ethers with diisocyanate, di-acid halide, or phosgene. The .alpha., .omega.-dihydroxy polyesters are obtained through trans-esterification of poly-(R)-(3)-hydroxy-butyric acid in the form of Biopol.RTM., and are thus degraded by means of an ester interchange catalyst, or catalysts, with degradation of the ester bonds. Biopol .RTM. is commercially available and is obtained in the form of a bacterial product. Other .alpha., .omega.-dihydroxy polyesters are produced through ring-opening polymerization of cyclic esters or lactones, for example .epsilon.-caprolactone with aliphatic diols.
The microstructure of the produced macrodiols results here depending on the monomer distribution, whereby stereospecific structures are produced exclusively.
The macrodiol is produced without or also with a catalyst, whereby SnO(Bu).sub.2 or dibutyl tin laurate is employed at temperatures of from 100.degree. to 160.degree. C.
Also polyurethanes are produced in this connection by reacting the macrodiols with diisocyanate such as, for example 1,6-hexamethylene diisocyanate, whereby the block polymers consisting of macrodiol and diisocyanate, other than with the present invention, always have valerate segments in the final product.
According to EP 0 696 605 A1, the bio-compatible or biodegradable polymers are used as medical implants, for which reason the material has to satisfy high technical requirements.
It is particularly disadvantageous in this connection that both the starting and the final products are stereo-specific, i.e. that only certain configurations are present (e.g., the bacterial product only has the R-configuration). Furthermore, bacterial polymers are, as a rule, very brittle because of their very regular crystal structure, and consequently very fragile. The polymeric products of EP 0 696 605 A1 are slightly softer, however, they still exhibit a brittle property to some extent. Furthermore, the bacterial starting products are relatively expensive. Moreover, said block polymers exhibit different discolorations, i.e. like their bacterial starting products, they are milk-colored, as a rule, which may give them a visually unattractive appearance. Said drawbacks limit the fields of application of the products of EP 0 696 605 A1 at least to some extent.
An attempt is made according to DE 195 08 627 A1 to avoid said drawbacks of the bacterially obtained PHA-material through the synthesis of polyester urethanes built up from diisocyanate and macrodiols, which in turn are produced from alkylene oxides and carbon monoxide. This method particularly has the drawback that the process has to be carried out with toxic and combustible gases under high pressure.